1. Field of the Invention
The present invention relates to the field of semiconductor manufacturing, and more particularly to the field of conditioning of polishing pads used for chemical-mechanical and other types of polishing.
2. Discussion of Related Art
In semiconductor manufacturing, chemical-mechanical polishing (CMP) is often used to ensure planar topography in the fabrication of integrated circuits and other semiconductor devices.
For one approach, a silicon or other semiconductor wafer is placed face down on a table covered with a flat pad that has been coated with slurry, an abrasive material. Both the wafer and that table are then rotated relative to each other to remove steps and other protrusions in the topography of the wafer. This abrasive polishing process continues until the surface of the wafer contacting the pad is largely planar.
One factor in achieving and maintaining a high and stable polishing rate is conditioning of the flat pad to maintain pad roughness. Over time, the initially rough and/or grooved surface of the flat pad is worn down due to polishing. Further, during polishing, the polishing pad has a tendency to glaze over due to build-up on the pad surface of slurry and other deposits.
A smooth pad surface results in a reduction of slurry delivery to the wafer surface causing low, unpredictable polish rates. Low polish rates decrease wafer throughput and make the planarization process difficult to control. Further, when the pad surface becomes "glazed" or smoothed through use, rough wafers are polished at a different, higher rate than smooth wafers.
To prevent glazing, the polishing pad is mechanically scored or "conditioned." Conditioning the pad removes the slurry/deposit build-up and roughens the surface of the pad. Different approaches to conditioning may be required depending on the hardness of the pad surface and the particular slurry used for polishing. Further, conditioning may be performed by a conditioning apparatus in a discrete conditioning step or during wafer polishing depending on the specific conditioning process and apparatus used.
An example of a conditioning apparatus 100 used for a discrete conditioning step is shown in FIG. 1. The apparatus 100 includes a conditioning block or bar 105 that is rotated concentrically about the axis 110 to condition the pad 120 when the conditioning block 105 is pressed against the pad 120. U.S. Pat. No. 5,611,943 to Cadien et al. and assigned to Intel Corporation, the assignee of the present invention, also describes an approach for conditioning pads between wafer polishing steps.
Diamond is a preferred pad conditioning surface material because of its durability, even in processes using very abrasive slurries. Pad conditioning surface materials that wear more easily than diamond may require frequent replacement and/or servicing of the scoring apparatus or pad conditioning block.
FIG. 2 shows a cross-section of one prior conditioning block 200, also referred to more generally as a scoring apparatus, that may be used with a conditioning apparatus such as the conditioning apparatus 100 of FIG. 1. The conditioning block 200 includes a block base 205 made of stainless steel having embedded stainless steel threaded shanks 210 and a wear plate 212 to prevent excessive wear to the conditioning block. The shanks 210 have diamond tips 215 braised or otherwise mounted on the threaded shanks 210. The shanks 210 are adjustable to control the extent to which the diamond tips 215 protrude from the block base 205 and the wear plate 212. A conditioning block including threaded shanks is described in U.S. Pat. No. 5,216,843 to Breivogel et al. and assigned to Intel Corporation, the assignee of the present invention.
The above-described approach, while effective in providing pad conditioning for pads having hard pad surfaces, has some drawbacks with respect to efficiency and cost. The threaded shanks 210 having the diamond tips 215 may require frequent adjustment with special tools by trained personnel. The adjustments themselves are subjective, and thus, may vary from person to person. Further, the diamond tips 215 must be flawless such that they do not easily chip during the polishing process. Consequently, this approach may be costly in terms of material and implementation.
FIG. 3 shows a cross-section of another prior approach for a conditioning block. The conditioning block 300 of FIG. 3 uses a diamond impregnated material or diamond grit 305 for pad conditioning. The conditioning block 300 of FIG. 3 may be used with the pad conditioning apparatus of FIG. 1 or another pad conditioning apparatus.
For this approach, there is a disadvantage in that the diamond grit 305 used to provide a pad conditioning surface easily separates from the pad conditioning block 300 as the adhesive 310 used to hold the diamond grit 305 in place wears. The loose diamond grit can cause scratching of the wafer and even contamination of other semiconductor materials in the vicinity of the pad conditioner because the diamond grit 305 is not made for use in a cleanroom environment.